The researchers noted previous attempts to control Britain's gray squirrel population had not stopped or slowed their spread, and culling might result in increased localized density, greater forest damage and more disease.

Bristol University Professor Stephen Harris, who led the study, said he's not against trying to protect red squirrels. "But if red squirrel conservation depends on killing grey squirrels, this is an extremely expensive, commitment," he told The Independent.

"Since all the past evidence suggests that this will not work, why waste more resources?" he asked. "And is it justifiable to enter on a slaughter policy that has no prognosis of success? There are alternative, and possibly better, approaches."